Calmodulin (CaM) a high affinity Ca(II) binding protein, is an important regulatory protein in eucaryotic cells. In addition, it has been implicated in neurotransmitter release and cell division. An understanding of how one protein can regulate so many diverse process is important in order to understand cellular processes and conversely the problems which may arise from improper regulation of the cells. Lanthanides (Ln(III)) are frequently used as probes for Ca(II) in the study of GaM. In order to interpret the relevance of such studies, it is essential to understand how well the Ln(III)-CaM complexes mimic the Ca(II)-CaM complex. THe suitability of lanthanides as models will be judged by three separate criteria. First, the ability of various lanthanides to cause activation of a CaM-dependent enzyme will be studied. The specific enzyme studied will be cyclic nucleotide phosphodiesterase, following previously described procedures (Buccigross et al, 1986). The second aspect will examine the ability of Ln(III)-CaM complexes to bind to various target molecules. These studies will be performed as titrations of apo-CaM with the specific metal to studied. The method of titration will be a variation of those previous described (Buccigross & Nelson, 1986; 1988). The binding of CaM to target molecules will be judged by fluorescence increases in the target molecules induced by CaM binding (Johnson & Wittenauer, 1986). The last aspect of the project will attempt to evaluate the overall conformation of the protein with various metal ions. This aspect of the study requires raising antibodies to Ca(II)-CaM and comparing their binding to the Ln(III)-CaM complexes, with that of the Ca(II)-CaM complex.